Primer Tm for sequencing

What is thought to be the optimal characteristics for
sequencing primers, specifically regarding Tm, GC clamping,
and primer self-annealing? I use alkaline conditions to
denature sequencing template in the standard Sequenase
way, but the availability of primer design software has
made me think that a more rational approach to sequencing
primer design is possible instead of the usual hit-and-miss
eyeball method.
Regards,
Chris